For many years, in the course of fisheries investigations, large numbers of fish have been marked by means of numbered metal tags. Other marking methods, such as dyeing, branding and clipping of fins, have all been tried but found to be either unsuitable, or difficult of application, or less satisfactory in some way. Since 1924 the Discovery Committee has marked some thousands of whales. For this purpose it has been found convenient to use stainless steel tubes which are fired into the blubber and remain firmly embedded until the whale is captured and dismembered by the whalers. Whale marking is in fact limited to this method, because these immense animals cannot be caught and later released. In the case of seals it is unlikely that marks shot into the blubber would prove successful because their skin and blubber is thinner than that of whales and, as seals haul out on land and ice at intervals, the mark would soon be torn out.